1. Field of the Invention
This invention relates to a hub unit (wheel-supporting rolling bearing unit) for supporting a wheel of an automobile or the like and a brake rotary member (for example, a brake rotor or a brake drum) rotating with this wheel.
2. Description of the Background Art
As a hub unit of this kind, there is known one including a hub ring 10, an inner ring 20, an outer ring 30, and a plurality of rolling members 40 as shown in FIG. 5.
A pilot portion 110 and a wheel-mounting flange 120 are provided at an outboard side (which is an outer end portion in a direction of a width of an automobile in a condition in which the hub unit is mounted on the automobile, and means a left end portion in FIG. 5) of the hub ring 10. A wheel and a brake rotor (brake rotary member) which are not shown are fixed to an axially outward side surface of this wheel-mounting flange 120 through bolts 60.
On the other hand, a smaller-diameter step portion 130 is formed at an inboard side (which is an inner end portion in the direction of the width of the automobile in the condition in which the hub unit is mounted on the automobile, and means a right end portion in FIG. 5) of the hub ring 10. The inner ring 20 is fitted on this smaller-diameter step portion 130. Inner raceway surfaces 10a and 20a are formed on an outer peripheral surface of an axially intermediate portion of the hub ring 10 and an outer peripheral surface of the inner ring 20, respectively.
An inboard-side distal end portion of the hub ring 10 is formed into a cylindrical tubular shape, and by caulkingly spreading this cylindrical tubular portion (caulking portion) radially outwardly, the inner ring 20, fitted on the smaller-diameter step portion 130 of the hub ring 10, is fixed in a predetermined position. In some cases, instead of the caulking, a necessary preload is applied to the inner ring 20 by fastening a nut.
A plurality of rows of outer raceway surfaces 30a and 30b, corresponding respectively to the inner raceway surfaces 10a and 20a of the hub ring 10 and inner ring 20, are formed on an inner peripheral surface of the outer ring 30. A suspension-mounting flange 310 is provided at that end portion of this outer ring 30 remote from the wheel-mounting flange 120 of the hub ring 10.
The plurality of rolling members 40 are rollably mounted between each of the inner raceway surfaces 10a and 20a, formed respectively on the hub ring 10 and the inner ring 20, and a respective one of the outer raceway surfaces 30a and 30b, formed on the outer ring 30, through a cage 50.
In FIG. 5, although an explanation has been made of the case where balls are used as the rolling members 40, tapered rollers are used as the rolling members 40 in some cases where the hub unit has a heavy weight.
For mounting the hub unit on the automobile, the suspension-mounting flange 310 of the outer ring 30 (which is the non-rotation side) is fixed to a suspension device (not shown), and the brake rotor and the wheel (which are not shown) are fixed to the wheel-mounting flange 120 of the hub ring 10 (which is the rotation side) through the hub bolts 60. As a result, the wheel can be rotatably supported on the suspension device.
Further, run-out P of a reference surface 2f1z of a flange 2fz relative to a rotation center Xo-Xo of a hub unit Huz is required in the market to be highly precise at the time of shipment so that a brake shudder problem will not arise.
However, muddy water is splashed on the hub unit Huz during the travel of the vehicle, and thus an environment in which this hub unit is used is severe. Therefore, when the reference surface 2f1z of the flange 2fz, made of carbon steel, is exposed to muddy water, rust can develop on this reference surface. In this case, there is a fear that the initial run-out P can not be kept highly precisely, so that the brake shudder problem arises.
There is a proposal for solving the problem with the rust of the hub unit in Japanese Patent Unexamined Publication No. JP-A-9-15256.
In the JP-A-9-15256, however, a thermosetting resin is coated on an outer peripheral surface of an outer ring of a hub unit, and a coating is formed so as to prevent rust from developing on a serrated portion forming a pulsar ring, and this is not designed to maintain the precision of flange run-out by preventing rust from developing on a wheel-mounting flange.
On the other hand, as means for suppressing the developing of run-out, there is given means for cutting the side surface of the wheel-supporting flange 120 after fastening the hub bolts 60. Although this means can suppress the generation of vibration, there is encountered a problem that fretting and rust develop on the side surface of the wheel-supporting flange 120.